The Barra Sonobuoy System

The Threat From Submarines

Submarines can wreak havoc on shipping and naval operations. In 1942 during World War II, three enemy midget submarines sneaked right into Sydney Harbour and sank a warship.

Elsewhere in that war submarines sank over 5,000 ships: Britain was nearly crippled by its losses in the Battle of the Atlantic and later Japan in turn suffered severe losses in the Pacific. More recently the Argentinian Light Cruiser General Belgrano was sunk by a British nuclear submarine during the 1982 Falklands War and in 2010 the Republic of South Korea corvette Cheonan was allegedly torpedoed by a North Korean midget submarine. Sea-going nations such as Australia clearly need a viable anti-submarine warfare capability.

Lurking beneath the sea surface, submarines are hard to detect: they cannot be seen or detected by radar and are very quiet. The Barra sonobuoy is a device that is dropped from specialised maritime patrol aircraft and uses hydrophones (underwater microphones) to listen for the faint sounds made by submarines. The sounds are then transmitted by a radio link to the aircraft where they are processed and displayed in real-time to provide the crew with information on the location and type of submarine.

The Barra sonobuoy system

Sonobuoys with a single hydrophone have been in use since the end of the Second World War - but with limited effectiveness. Recognising the shortcomings of the existing systems, Australian defence researchers Alan Butement and Henry d'Assumpcao in 1964 proposed a much more sophisticated sonobuoy consisting of many hydrophones arranged in a horizontal plane. This was given the name BARRA (a word in one of the indigenous Australian languages meaning “listening”).

Implementing this idea was extremely difficult because hundreds of components had to be packaged inside the same volume as the much simpler single-hydrophone sonobuoy. Experienced defence engineers in Britain and America thought it could not be done, and certainly could not be manufactured at an affordable cost and work reliably. In addition, the airborne real-time signal processing would have to be many times more complex than that for the simpler sonobuoys.

Australian DSTO mechanical and electronic engineers achieved a breakthrough by fitting twenty-five hydrophones and all the other electronic equipment inside the standard sonobuoy container. Not only can the Barra sonobuoy detect weaker sounds than the simpler sonobuoys but it can also determine where the sounds are coming from by beamforming the planar array of hydrophones. It was also established that it would be feasible to carry all the high-speed signal processing equipment in the aircraft.

Britain saw the advantage of the Australian approach and signed an agreement under which Australia would develop the sonobuoy and Britain the airborne real-time signal processing system for RAF (UK) and RAAF (AUS) maritime patrol aircraft.

Barra – the success story

For over 30 years Barra has been, arguably, the most advanced sonobuoy system in the world, and has made a major contribution to defence capability in Australia and overseas. It was used by the (UK) Royal Air Force in the Falklands war in 1982 and is still in use by the Royal Australian Air Force and the RAF.

The project has also made a significant contribution to the economy and to employment. More than 30,000 sonobuoys have been produced in over 30 years of manufacturing with total contracts estimated at $500M (in 2010 Australian dollars).

Developments continue: research is underway in DSTO and Thales Australia (manufacturer of BARRA sonobuoy) to add a sound source to transmit a signal so that the Barra sonobuoy can receive the echoes from submarines. In this way, even if submarines can be made much quieter, they cannot altogether escape detection.